The present invention relates to a pump with variable parameters.
Pumps with variable parameters for water and two-phase flow are necessary particularly because in the industry the liquid supply from technological processes to the pump facility is variable and is periodically limited. In industrial pumping systems there is always a danger that the pumps will lose prime, or cavitate and wear intensively. Therefore, it is necessary to use external means to throttle the pump discharge, or to deliver additional waste water to the pump suction to prevent the stoppage and intensive wearing of the pump.
Pump throttling is by far the most frequently used means to vary the pump capacity. However, as is known, throttling the pump discharge results in great waste of power. Pump capacity variation can be obtained by changing the rotation speed of the drive. This however can be realized by using engine or turbine drive, or electric motors with special electric system facilities for various speeds, which is complex and expensive.
Therefore, one of the major unsolved problems in centrifugal pumps is designing a pump which is able to self-regulate the working parameters automatically without using external means.
It is known that for regulating the capacity of centrifugal pumps one uses adjustable diffusion vanes arranged in the impeller or in the casing. This arrangement shows an appreciable gain in efficiency at reduced capacity. However, because of mechanical complications this method has not become practical.
The present invention involves a principle comprising a change in the geometry of the impeller and casing for varying the pump""s capacity and pressure.
A patent and literature search reveals the existence of American designs which involve a method of changing the impeller geometry for varying pump capacity. A variable centrifugal pump design is presented in a General Electric Company U.S. Pat. No. 3,784,318 in which the pump capacity is varied by covering a part of the impeller outlet width by a cylindrical throttle positioned between said impeller and the casing diffuser vanes. In U.S. Pat. No. 4,527,949, the pump capacity of a centrifugal machine is varied by adjusting the diffuser passage between a fixed wall and an opposed, movable wall.
However, the mechanical complications make these direct methods impractical, especially for pumping suspensions with abrasive and other solid components. Another disadvantage is that great casing hydraulic losses are incurred when impeller discharge is reduced while the casing diffuser chamber volume and inlet size remain unchanged. It is known that casing hydraulic losses are the most considerable factor in the pump efficiency balance.
Other patented designs similar to the present one under consideration, are those of turbocompressor radial diffusers presented in U.S. Pat. Nos. 2,996,996 and 3,032,259.
Thus, in U.S. Pat. No. 2,996,996 a radial diffuser is presented for a radial turbomachine having a movable wall and an apparatus having a plurality of guide vanes enabling it to regulate this apparatus inside the diffuser for reducing losses. In U.S. Pat. No. 3,032,259 a turbocompressor is presented having a radial diffuser which has a passage adjacent the casing outlet chamber. One wall of this passage is movable after a rotary motion of a ring element.
As to gas turbocompressors, diffuser guide vane apparatus with adjustable vanes are used to reduce losses at the change of the compressor discharge. In hydraulic pumps, by contrast to turbocompressores, radial diffusers with guide vanes are used only in exclusive cases. Such a case has been analyzed above.
Since pumps function by liquid, which is a non-compressible medium, its movement in the diffuser is connected with vortex formations at the change of the pump discharge. As a consequence, hydraulic losses in the pump diffuser (outlet chamber) are significantly greater than in the compressor diffuser where gas is a compressible medium. As a result, the greatest losses in balance power of the pump lies with the outlet chamber (diffuser). Therefore, there is a problem of reducing hydraulic losses in the pump outlet chamber when its discharge is variable.
The object of the present invention is to provide an efficient centrifugal pump having variable capacity and pressure the overcomes the drawbacks and disadvantages of that prior art. The invention solves in a novel manner the problem of changing the pumping parameters allowing one to obtain the desired capacity and pressure under changing conditions so as to maintain its pumping efficiency and minimize energy losses. This is achieved by providing a set of movable controlling sideplates as supplementary walls inside the outlet chamber, movable axially along the impeller. Their position changes the outlet width of the impeller and simultaneously the chamber volume, allowing one to obtain the desired pumping parameters. This new design is advantageous since the impeller outlet width is partly changed and the pump discharge is reduced, the volume of the casing is also reduced correspondingly. This prevents the creation of vortex flow in the casing chamber under changing parameters. In addition, the controlling sideplates are designed such that the movement of the flow in the casing outlet chamber is in the form of a double inward spiral which is optimal for the prevention of vortex flow and in particular for reducing wear when pumping abrasive suspensions. Both the control of the chamber volume by the sideplates and the shape of the sideplates causing the spiral motion, prevent vortex formation and improves the efficiency of the pump while varying its parameters.
In the design a driving mechanism is connected to the controlling sideplates for their axial movement. The invention contains driving mechanisms that are of the hydraulic type or electrical type according to the convenience of the user. The hydrodriving mechanism is achieved in two different designs: one external to the casing and the other arranged internally being incorporated into the controlling sideplates. The internal hydrodriving mechanism has also one of its embodiments wherein the controlling sideplates are elastic (such as rubber) and is part of the casing inner liner. The inner lining of the sideplates protects the casing from wear, particularly when handling abrasive suspensions.
The pump""s parameters are varied automatically. To achieve this, a driving mechanism is included in a control system whose main purpose is to move the controlling sideplates automatically and thus control the variable pumping parameters.